Single-chip optical coherence tomography device

Abstract

A high-performance single-chip, integrated-optics-based OCT system is disclosed, where the length of the reference arm is digitally variable. The reference arm includes a plurality of switch stages comprising a 2×2 tunable wavelength-independent waveguide switch that can direct an input light signal onto either of two different-length output waveguides. In some embodiments, the directional couplers are thermo-optic based. Some embodiments include a solid-state scanning system for scanning a sample signal along a line of object points on the sample under test.

What is claimed is: 
     
       1. An integrated-optics-based optical coherence tomography (OCT) system having a sample arm and a reference arm, the OCT system comprising a photonic lightwave circuit (PLC) that is monolithically integrated on a substrate, wherein the PLC includes:
 (i) a coupler for distributing an input light signal into a sample signal on the sample arm and a reference signal on the reference arm; 
 (ii) a beam combiner for combining the reference signal and a reflected signal from a sample to generate an interference signal, the reflected signal being based on the sample signal and the sample; and 
 (iii) the reference arm, wherein the reference arm is operative for conveying the reference signal from the coupler to the beam combiner, and wherein the reference arm includes a delay controller that is operative for digitally controlling the length of the reference arm within a range from a minimum length to a maximum length; 
 a first photodetector configured to provide an output signal based on the interference signal; 
 a second photodetector configured to provide a dispersion signal that is based on a first signal received from the delay controller, wherein the first signal includes at least a portion of the reference signal; and 
 a processor that is operative for compensating a dispersion mismatch between the reference arm and sample arm based on the dispersion signal. 
 
     
     
       2. The system of  claim 1  wherein the delay controller is also operative for controlling the optical power of the reference signal received at the beam combiner. 
     
     
       3. The system of  claim 1  wherein the OCT system further includes:
 (iv) a first waveguide for conveying the sample signal from the coupler to the sample; and 
 (v) a second waveguide for receiving a reflected signal from the sample and conveying the reflected signal to the beam combiner, the reflected signal being based on the sample signal and the sample. 
 
     
     
       4. The system of  claim 1  wherein the delay controller comprises a plurality of switch stages, each switch stage including:
 a first waveguide portion having a first length; 
 a second waveguide portion having a second length that is different than the first length; and 
 a waveguide switch that is operative for optically coupling a light signal received at a first input port to either of the first waveguide portion and the second waveguide portion. 
 
     
     
       5. The system of  claim 4  wherein each waveguide switch includes:
 a delay section that includes a trunk waveguide and a delay waveguide, wherein the delay section is operative for controlling cross-coupling between the trunk waveguide and the delay waveguide based on a control signal; 
 wherein the trunk waveguide is optically coupled with one of the first waveguide portion and the second waveguide portion; and 
 wherein the delay waveguide is optically coupled with the other one of the first waveguide portion and the second waveguide portion. 
 
     
     
       6. The system of  claim 5  wherein each waveguide switch further includes:
 a first directional coupler; and 
 a second directional coupler; 
 wherein the delay section is between the first and second directional couplers; and 
 wherein the first and second directional couplers are complimentary directional couplers. 
 
     
     
       7. The system of  claim 4  wherein at least one waveguide switch of the plurality thereof is operative for controlling the portion of its respective light signal that is optically coupled into each of the first waveguide portion and the second waveguide portion based on a thermo-optic effect. 
     
     
       8. The system of  claim 1  wherein the beam combiner is operative for combining the reference signal and the reflected signal based on two-mode interference. 
     
     
       9. The system of  claim 1  wherein the PLC further includes a beam scanner that is operative for providing the sample signal to a plurality of object points on the sample, wherein the beam scanner comprises:
 a plurality of waveguides, each waveguide including a facet, wherein the plurality of facets collectively defines an output port; and 
 a plurality of waveguide switches, wherein each waveguide switch of the plurality thereof is operative for switching light between a different pair of waveguides of the plurality thereof; 
 wherein a first waveguide of the plurality of waveguides is dimensioned and arranged to receive the sample signal from the coupler. 
 
     
     
       10. The system of  claim 9  wherein the facets of the plurality thereof are uniformly spaced. 
     
     
       11. A method for performing optical coherence tomography (OCT), the method comprising:
 providing a planar-lightwave circuit (PLC) that includes a coupler, a reference waveguide, a delay controller, and a beam combiner, wherein the PLC is monolithically integrated on a substrate; 
 distributing an input light signal received at the coupler into a sample signal on a sample arm and a reference signal on a reference arm, wherein the reference arm includes the reference waveguide and the delay controller; 
 providing the sample signal to a sample; 
 receiving a reflected signal at the beam combiner, wherein the reflected signal is based on the sample signal and the sample; 
 conveying the reference signal from the coupler to the beam combiner via the reference waveguide and the delay controller; 
 combining the reference signal and the reflected signal at the beam combiner to generate an interference signal; 
 providing an output signal from a first photodetector, wherein the output signal is based on the interference signal; 
 controlling the delay controller to digitally control a length of the reference arm within a range from an initial length to a maximum length; 
 directing a dispersion signal to a second photodetector, wherein the dispersion signal includes at least a portion of the reference signal; and 
 compensating a dispersion mismatch between the reference arm and sample arm based on the dispersion signal. 
 
     
     
       12. The method of  claim 11  further comprising controlling the optical power of the reference signal received at the beam combiner. 
     
     
       13. The method of  claim 11  further comprising providing the beam combiner such that it is operative for combining the reference signal and the reflected signal based on two-mode interference. 
     
     
       14. The method of  claim 11  wherein the length of the reference arm is controlled by controlling the length of the delay controller. 
     
     
       15. The method of  claim 14  further comprising:
 providing the delay controller such that it includes a plurality of switch stages, wherein each switch stage comprises:
 (i) a first waveguide portion having a first length; 
 (ii) a second waveguide portion having a second length that is different than the first length; and 
 (iii) a waveguide switch that is operative for optically coupling a first light signal received at a first input port to either of the first waveguide portion and the second waveguide portion; and 
 
 providing a control signal to each waveguide switch of the plurality thereof to control the optical coupling of its respective input port with each of its respective first and second waveguide portions. 
 
     
     
       16. The method of  claim 15  wherein the delay controller is provided such that at least one waveguide switch of the plurality thereof includes a delay section that includes a trunk waveguide and a delay waveguide, wherein the delay section is operative for controlling cross-coupling between the trunk waveguide and the delay waveguide based on the control signal provided to its respective waveguide switch. 
     
     
       17. The method of  claim 16  wherein the delay controller is provided such that at least one waveguide switch of the plurality thereof further includes a first directional coupler and a second directional coupler, wherein the first and second directional couplers are complimentary directional couplers, and wherein the delay section is between the first and second directional couplers. 
     
     
       18. The method of  claim 15  wherein at least one waveguide switch of the plurality thereof is provided such that it is operative for controlling the portion of its respective light signal that is optically coupled into each of the first waveguide portion and the second waveguide portion based on a thermo-optic effect. 
     
     
       19. The method of  claim 11  further comprising providing the sample signal to each of a plurality of object points on the sample by operations comprising:
 conveying the sample signal from the coupler to a beam scanner that includes a plurality of waveguides, a plurality of waveguide switches, and an output port comprising a plurality of facets, wherein each waveguide of the plurality thereof includes a different facet of the plurality thereof, and wherein each waveguide switch of the plurality thereof is operative for switching light between a different pair of waveguides of the plurality thereof; and 
 controlling the plurality of waveguide switches such that the sample signal is provided to each object point of the plurality thereof from a different facet of the output port. 
 
     
     
       20. The method of  claim 19  further comprising providing the beam scanner such that the facets of the plurality thereof are uniformly spaced.